TEM Investigation on the Adhesion of YPSZ EB-PVD TBCs

Spallation sensitive as-coated EB-PVD TBC systems on Nimonic 75 substrates were investigated by TEM. Decohesion was observed within the thermally grown oxide (TGO) layer between NiCoCrAlY bond coat and TBC. The TGOs consisted of unexpected oxide phases. In one case the TGO consisted of stratified layers containing spinel phase and chromia. In another case the TGO contained a vitreous Ca-silicate and a crystalline Y-silicate two-phase interlayer. The generation of the respective oxides is initiated by processing steps before TBC deposition. Suggestions for the manufacture of more confident TBC systems are presented. (Author)